1. Field of the Invention
The present invention relates to a method of manufacturing packages, a bonded wafer member, a piezoelectric vibrator, an oscillator, an electronic apparatus, and a radio timepiece.
2. Description of the Related Art
In recent years, a piezoelectric vibrator using crystal or the like is used as a time instance source, a timing source for control signals or the like, and a reference signal source or the like in mobile phone sets or portable information terminal devices. Various types of such piezoelectric vibrators are known, and a surface mount (SMD) type piezoelectric vibrator is known as one of these piezoelectric vibrators. The piezoelectric vibrator of this type includes, for example, a base substrate and a lid substrate bonded to each other, and a cavity formed between these substrates, and a piezoelectric vibration reed (content) stored in the cavity sealed in an air-tight manner.
Here, when manufacturing the piezoelectric vibrator described above, as shown in Patent Documents 1 and 2, for example, a depressed portion for a cavity is formed on a lid substrate wafer (second wafer) and a piezoelectric vibration reed is mounted on a base substrate wafer (first wafer), and then the both wafers are bonded to form a bonded wafer member formed with a plurality of packages arranged in row and column directions of the wafers. Then, by cutting the bonded wafer member into individual packages (individual cavities) formed on the bonded wafer member, a plurality of piezoelectric vibrators (packages) each having a piezoelectric vibration reed airtightly sealed in the cavity are manufactured.
Incidentally, as methods of cutting the bonded wafer member, methods employing, for example, a blade or a laser or the like are known.
However, the method of cutting using the blade has problems such that cutting margins are needed to provide between the cavities considering the width of the blade, and that chippings are generated at the time of cutting and cutting surfaces are coarse or the like.    Patent Document 1: JP-A-2002-121037    Patent Document 2: JP-A-2007-13628
Here, a method of cutting a bonded wafer member using a laser will be described in brief. FIG. 18 is a plan view of a bonded wafer member for explaining a method of cutting using a laser in the related art. For reference sake, a broken line L in the drawing is a contour line when a package is irradiated with a laser along a contour thereof, and a solid line L′ shows a scribe line formed when being irradiated actually with the laser.
As shown in FIG. 18, a bonded wafer member 150 is provided with respective cavities 153 formed between both substrate wafers 151, 152 and arranged in a plurality of rows and plurality of columns along the direction of plane except for an outer peripheral portion of the bonded wafer member 150. Then, piezoelectric vibration reeds (not shown) are mounted respectively in the respective cavities 153 to constitute a plurality of piezoelectric vibrators. Incidentally, the outermost peripheral portion of the bonded wafer member 150 is an area where the cavities 153 are not formed because it is used for clamping or the like when bonding the both substrate wafers 151, 152, for example. In other words, in the bonded wafer member 150, the area of the outer peripheral portion where the cavities 153 are not formed corresponds to a non-cavity formed area Y′ and an inside area surrounded by the non-cavity formed area Y′ corresponds to a cavity formed area X′ having the cavities 153.
Then, when cutting the bonded wafer member 150 by the laser, for example, a front surface of the substrate wafer 151 on one side is irradiated and scanned with a laser and formed with grooves (scribe line) having a predetermined depth, and then an impact is applied to the substrate wafer 152 on the other side along the scribe lines from a back surface thereof, thereby braking and cutting the same. In this manner, a plurality of the piezoelectric vibrators can be manufactured at once from the bonded wafer member 150. In this case, the method of cutting using a laser has such advantages that the cutting margin is significantly smaller than that in the method of cutting using a blade, that the cutting speed is high, and the coarseness of the cutting surfaces are preferable or the like.
Incidentally, when the laser is scanned along contour lines L, in the cutting step described above, desired scribe lines L′ can be formed along the contour lines L in a center portion of the cavity formed area X′.
However, there is a problem that the scribe lines L′ are curved with respect to the contour lines L because of the reason such that energies given by the laser vary or the like in the vicinity of a boundary portion from the cavity formed area X′ to the non-cavity formed area Y′.
If the scribe lines L′ are curved inside the non-cavity formed area Y′, there arises a problem that the piezoelectric vibrators cannot be cut into a predetermined size in the outermost peripheral portion of the wafer 152. In other words, since the scribe lines L′ may be formed on the cavities 153, for example, the interiors of the cavity 153 and the outside may communicate after having cut the bonded wafer member 150, so that the interiors of the cavities 153 may not be hermetically sealed.
Consequently, there arises a problem that the number of the piezoelectric vibrators taken out as conforming articles from a single bonded wafer member 150 is lowered with respect to the piezoelectric vibration reeds mounted in the cavities 153, so that the process yield is lowered.